1. Field of Invention
This invention relates to substituted polybenzimidazole articles and a process for their production. More particularly, the invention relates to the sulfonation of hydroxyethylated polybenzimidazole fibers and a process for their production.
2. Prior Art
Polybenzimidazoles are a known class of heterocyclic polymers which are characterized by a high degree of thermal and chemical stability. Processes for their production are disclosed in U.S. Re. 26,065, and U.S. Pat. Nos. 3,313,783, 3,509,108, 3,555,389, 3,433,772, 3,408,336, 3,549,603, 3,708,439, 4,154,919, and 4,312,976. (All patents enumerated herein are incorporated by reference.)
Shaped articles, such as fibers, produced from polybenzimidazole polymers can be quite useful for a broad range of applications, such as electrodialysis, reverse osmosis, and ultra filtration. However, because the pore size of these unsubstituted polybenzimidazole shaped articles is quite small, i.e. less than about one angstrom, the shaped articles cannot be used as filters for molecules having molecular weights greater than about 1000.
Further, although polybenzimidazole polymers are generally more resistant to chemical reaction than other types of polymers, such as cellulose acetate polymers, reaction at the imidazole nitro-hydrogen bond on the polybenzimidazole polymer will under certain conditions, thereby adversely affecting the performance of the polybenzimidazole polymer.
One method of reducing the reactivity of the polybenzimidazole polymer is by replacing the imidazole hydrogen with a less reactive substituent. Several processes for the production of such substituted polybenzimidazole polymers have been disclosed. For example, one process for producing the hydroxyethylated polybenzimidazole polymers used in this application is disclosed in U.S. Pat. No. 4,599,388. However, the '388 patent fails to disclose either a process for the sulfonation of hydroxyethylated polybenzimidazole polymers or a process for the production or sulfonation of hydroxyethylated polybenzimidazole fibers.
U.S. Pat. No. 3,578,644 also discloses a process for the production of hydroxyl-substituted polybenzimidazole polymers, by the reaction of a polybenzimidazole polymer with an omega-haloalkanol or a 1, 2 alkylene oxide in the presence of a basic catalyst. However, this reaction produces undesirable organic salts as a by-product and requires a pressurized vessel for the reaction. In addition, the types of polybenzimidazole polymers which can be used in the reaction are limited, because the bridging groups between the reactive imidazole rings of many polybenzimidazole polymers sterically hinder the reaction. As a result, polybenzimidazole polymers such as poly-2,2'(m-phenylene)-5,5'-bibenzimidazole and other similarly structured polybenzimidazole polymers, may not be used in this reaction Further, the '644 patent fails to disclose any process for the sulfonation of hydroxyethylated polybenzimidazole polymers or the production of hydroxyethylated polybenzimidazole fibers.
Additional processes for the production of substituted polybenzimidazole polymers or their products include: U.S. Pat. No. 4,579,915, wherein the imidazole hydrogen is replaced by an aromatic substituent corresponding to the formula: ##STR1## where R is nitro, cyano, or trifluoromethyl and R' is hydrogen, alkyl, nitro, cyano or trifluoromethyl; U.S. Pat. No. 4,377,546 which discloses a phenol substituted polybenzimidazole polymer; U.S. Pat. No. 3,943,125 which discloses a vast array of substituted tetraamino heterocyclic compounds; and U.S. Pat. No. 3,518,234 which discloses N-aryl substituted polybenzimidazole polymers. However, none of these patents disclose hydroxyethylated polybenzimidazole polymers, a process for their production, a process for sulfonation of hydroxyethylated polybenzimidazole polymers or a process for the production of hydroxyethylated polybenzimidazole fibers.
Another method of reducing the reactivity of polybenzimidazole polymers is by chemically modifying unsubstituted polybenzimidazole polymers, as is disclosed in U.S. Pat. No. 4,020,142. Technical reports published by Celanese Research Company (AD-755356, dated January, 1974) and Fabric Research Laboratories (AFML-TR-73-29, dated December, 1971) disclose a process for sulfonating unsubstituted polybenzimidazole fibers in order to reduce their thermal shrinkage. However these processes are significantly different from that disclosed in the instant invention.
Of particular interest in the preparation of useful polybenzimidazole shaped articles have been processes for the production of polybenzimidazole fibers. Polybenzimidazole fibers are produced by two basic processes, dry spinning, which involves spinning a polybenzimidazole polymer solution through a spinneret into an evaporative environment and wet spinning. In wet spinning, the spinning solution is spun through a spinneret either directly into a coagulation bath, wet jet/wet spinning, or through an air gap into the coagulation bath, dry jet/wet spinning. Typical dry spinning processes are disclosed in U.S. Pat. Nos. 3,584,104 and 3,502,756, while typical wet spinning processes are disclosed in U.S. Pat. Nos. 4,512,894, 4,263,245, 3,851,025, 3,619,453, 3,526,693 and 3,441,640.
While the processes for the production of polybenzimidazole fibers and the fibers produced by those processes may vary considerably, based on such factors as the composition of the coagulating bath, the denier of the spun fiber, or the structure of the fiber, none of the prior art patents disclose a method for spinning fibers formed from substituted polybenzimidazole polymers, in general, or hydroxyethylated polybenzimidazole polymers, in particular.
Accordingly, it is an object of the present invention to disclose a process for the preparation of sulfonated, hydroxyethylated polybenzimidazole fibers.
It is a further object of this invention to disclose a process for the preparation of sulfonated, hydroxyethylated polybenzimidazole fibers which are covalently bonded.
It is a still further object of this invention to disclose a process for the preparation of sulfonated, hydroxyethylated polybenzimidazole fibers that exhibit high chemical and thermal stability.
It is an additional object of this invention to disclose sulfonated, hydroxyethylated polybenzimidazole fibers which exhibit cation selectivity for electrodialysis and other electrochemical applications.
These and other objects, as well as the scope, nature and utilization of the process and the products produced by that process will be apparent to those skilled in the art, from a review of the following detailed description and appended claims.